Approximately 1% of live births in the United States weigh less than 1500 grams and are termed low birth weight (VLBW) infants. Advances in medical care have increased survival from 25% in 1969 to 85% in 1988. One of the advances allowing for improved survival can be attributed to improvements in nutritional management and the judicious use of total parenteral nutrition (TPN). Because of their small size, nutritional monitoring has not been practical; therefore, nutrient needs of this group of infants is based on data derived from term gestation infants or older children. Our laboratory has developed methods to accurately monitor vitamin B2 and B6 in these small infants requiring TPN. Preliminary data indicate that the manufacturer's recommended dosage results in a 100-400 fold increase in plasma riboflavin and marked increases in plasma B6 vitamers were also noted with the current recommended dose of pyridoxine. Both findings appear to be due in part to renal and hepatic immaturity. We are concerned that the persistent elevation in plasma levels of these vitamers coupled with deficient plasma and liver retinol may have deleterious effects on the VLBW during this critical stage of development. We feel strongly that more appropriate dosages should be defined immediately. Since correlations with classic blood chemistry changes or clinical signs of deficiency or toxicity are unlikely because of inherent complications associated with extreme immaturity, blood levels of the vitamins are felt to be the most appropriate method to determine efficacy of vitamin dosages. We propose to develop dose-response data for vitamins B2 and B6 using three dose levels in short-term (7-day studies). The initial dosage of both vitamins will utilize recently published recommendations for vitamins in VLBW infants. Long-term studies in 30 VLBW infants will evaluate the dose derived from the short-term studies. Because renal maturation after 15 days of life may alter urinary excretion and affect blood vitamin concentrations, the long- term studies are necessary and will include simultaneous urinary measurements. Since no comparative data in enterally fed VLBW infants are available, a series of 40 enterally fed VLBW infants will be evaluated during the first 38 days of life. These studies will therefore provide the data upon which to derive appropriate doses of vitamins B2 and B6 in VLBW infants who require TPN as well as to provide data which will be useful in projecting appropriate vitamin needs for enterally fed VLBW infants.